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Tuesday, April 10, 2012

Dynamically Allocate T1 Service

T1 lines have been used for decades to carry both voice and data. It’s commonly assumed that you need to specify which you are going to transport prior to installing the line. If you want voice, a channelized T1 line or ISDN PRI configuration is ordered. Each of the 23 or 24 channels will handle one telephone conversation. On the other hand, if you want a point to point T1 data line or dedicated Internet access, then you order a clear channel T1 line so you can use the entire 1.5 Mbps as a single pipe.

Many companies have multiple T1 lines installed because they need both high volume telephone service and dedicated Internet access. They may also have T1s available as dedicated private lines to branch offices or other business locations. All of these lines are ordered and configured separately. Is there any possibility of combining functions?

Indeed, there is. Let’s consider the channelized T1 line. Each of the 24 channels is independent and can carry one digitized voice call or 64 Kbps of data. The line doesn’t know or care what those bits represent. At each end, you have to know which channels are voice and which are data. The voice calls are all separate, of course. The data channels can be combined into one larger stream.

Early implementations of combined voice and data or integrated T1 lines did exactly that. They set up a channelized T1 line so that some channels were used to support business telephone calls and some were used for broadband data. Let’s say we simply divide the line capacity in half. That way 12 channels are used for 12 business phone lines. The other 12 are used for dedicated Internet access. 12 channels times 64 Kbps per channel gives you 768 Kbps of broadband service.

Why go to this trouble? A considerable portion of the cost involved in provisioning a T1 line is the local loop. That’s the twisted pair copper wires that run from your building to the telephone company central office. From there they can go to a competitive service provider or the phone company can use them for its own services. If a competitor wants the line they have to pay the phone company a lease fee that is passed along to you as a loop charge. Every time you add a T1 line you add an additional loop charge. If you can get one T1 line to do two functions, you only pay that loop charge once.

Integrated T1 service works well for smaller businesses that don’t need more than 12 outside phone lines or high bandwidth Internet service. Many smaller retailers use the data capability for credit card verification and for inventory control and other back office functions with headquarters. That plus telephone service takes care of their needs.

One glaring inefficiency in using a T1 line this way is that allocations are fixed. Any of those phone channels not in use simply sit there idle. That seems like a waste, since that idle bandwidth could help speed up Internet traffic if it was available. This is why newer implementations of integrated T1 use a different technology. Instead of dealing with all those channels independently, they convert the phone calls to packets and merge them with the data packets from the computer network. The combined data stream fills the T1 capacity of 1.5 Mbps. There is no idle capacity. Everything that isn’t voice is used for data.

Of course, for this to work the latency and congestion sensitive voice packets must have priority over the less critical data packets. That’s exactly what is done using Class of Service tagging. Voice packets always get higher priority. Whatever capacity they don’t use is automatically available for broadband data. This process is called dynamic allocation of bandwidth.

If that sounds a lot like the way a SIP trunk works, it’s because that’s exactly the way it is organized. In fact, SIP trunking is the new Integrated T1. Small SIP trunks use T1 lines, but you can also get higher capacity trunks using bonded T1, Ethernet over Copper, DS3, OC-3 or Ethernet over Fiber. The line works the same way on all of these. It is only the bandwidth that is different.

Could your business benefit from the cost savings of using a single Integrated T1 or SIP Trunk to supply both telephone and broadband Internet service, while maintaining excellent voice quality? If so, get prices and availability of dynamic line services like SIP trunks and Integrated T1.

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Telexplainer Google+ is a business-to-business service of T1 Rex and was formerly known as "T1 Rex's Business Telecom Explainer." Our mission is to offer technical and business information related to telecommunications and computer networking. We are teamed with Telarus, Inc. as our broker for worldwide telecom services, and are affiliates of other commercial services. Many images are used under license from Animation Factory or courtesy of Wikimedia Commons. Some are available on products from the Gigapacket Tech Store on Zazzle. Written and published by John Shepler. Profile+ You may contact me by sending email to: John (at) Telexplainer.com View John Shepler's profile